The invention relates to a process for removing the screw from the screw cylinder of a screw-type injection molding machine wherein the drive device for the screw is released from the rear end of the screw cylinder and the screw is withdrawn rearwardly from the opened screw cylinder. The invention also concerns a screw-type injection molding machine which is of a suitable configuration for carrying out the screw removal process. Finally the invention is concerned with an auxiliary apparatus for carrying out the process.
Removal of the screw of a screw-type injection molding machine is an operation which has to be repeatedly carried out in operation for the purposes of servicing, for the purposes of replacing the screw by a screw of a different geometry or size and also for the purposes of dealing with damage. In order to make the removal operation as easy as possible for the user, the screw-type injection molding machine must already be structurally designed for that purpose. The most usual procedure involved in removing the screw provides for a pivotal movement of the complete injection unit comprising a screw cylinder with the screw therein and the drive device for the screw, which is arranged behind the screw cylinder, about a vertical pivot axis which is disposed approximately at the longitudinal center of the injection unit. The pivotal movement is produced in such a way that the front end of the screw cylinder (injection end) faces towards the operating side of the injection molding machine and is accessible for the purposes of removing the cylinder head. By actuating the drive device for the axial stroke movement of the screw, that is to say the hydraulic injection cylinder, the screw can be pressed out forward through the open end of the cylinder and then withdrawn. However, in injection molding machines of medium size, as a result of the pivotal movement of the entire injection unit towards the side, the above-indicated procedure requires a comparatively large amount of space and, in relation to larger injection molding machines in which the injection unit already only be applied by a drive means which is specifically provided for that purpose. That drive means involves an additional amount of apparatus expenditure and in addition - if for reasons of saving space it must first be mounted in position prior to the operation of removing the screw - it takes up an additional amount of time. Added to that is the fact that removal of the screw forwardly through the screw cylinder is possible only when the diameter of the drive end of the screw which is generally provided with a tapered spline arrangement permits it. Having regard to the torques to be transmitted however the spline arrangement would frequently have to be larger in diameter than the inside diameter of the screw cylinder so that a compromise which in itself is undesirable must be made in regard to the load-carrying capacity of the spline arrangement if it is to be possible to carry out the operation of removing the screw in the above-described manner.
A screw removal process is also known in which the screw is withdrawn rearwardly from the screw cylinder so that there is no need to dismantle the cylinder head and also pivot the injection unit. With that process however the complete screw cylinder must be separated from the drive device so that the rear end of the cylinder and the screw are made accessible. That is very expensive and particularly when dealing with large injection molding machines, cannot be carried out without mechanical aids, because of the high weight of the screw cylinder.